This application is based on Japanese Patent Application HEI 11-287336, filed on Oct. 7, 1999, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
This invention relates to a shape and a structure of an on-chip micro-lens formed in a solid-state imaging device in order to input light efficiently.
b) Description of the Related Art
In a solid-state imaging device having a multiplicity of photoelectric conversion units formed on a semi-conductor substrate in a matrix shape, a light shielding film is formed on the substrate. The light shielding film has openings, each of which corresponds to each of the photoelectric conversion units formed on the substrate. A micro-lens is formed just above each opening of the light shielding film to increase the efficiency of the light concentration.
FIG. 6 are enlarged cross sectional views of a part of the solid-state imaging device according to the prior art.
Photoelectric conversion units 2 and transfer channels 3 are formed on a semi-conductor substrate 1 made of silicon. A partition region 4 is formed next to each transfer channel 3. After that, an upper surface of the semi-conductor substrate 1 having the photoelectric conversion units 2, the transfer channels 3 and the partition regions 4 are oxidized to form an insulating film 5 made of silicon oxide or the like.
Next, a transfer electrode is formed above each transfer channel 3, and an insulating film 5a is formed on the substrate 1 covering the transfer electrodes 5a. A light shielding film 7 having openings is formed on the insulating film 5a to shade the transfer electrodes 5a. Each opening of the light shielding film 7 is formed just above each photoelectric conversion unit 2.
On the light shielding film 7, a focus adjusting layer 8 including a passivation layer, and then a color filter layer 9 is formed thereon.
A planarizing layer 10 is formed on the color filter layer 9, and thereon a lens layer 11 made of transparent resin is formed by the spin-coat. The lens layer 11 is patterned by the photolithography to make a shape shown in FIG. 6A.
Then, to make the patterned lens layers 11 into micro-lenses 11, each having a shape shown in FIG. 6B, by flowing with heating process at a temperature beyond a softening temperature of the transparent resin used for forming the lens layers 11.
A commonly used imaging sensor for camcorders and digital still cameras has over one million pixels. In this kind of multi-pixel imaging sensor, a size of an on-chip micro lens is less than about five micrometers around, and is getting nearly three micrometers around. The size of that kind of imaging sensor is less than a quarter of a size of an old imaging sensor.
As a pixel gets smaller, an on-chip micro lens gets smaller, too. Shrinking of the on-chip micro lens makes a radius of curvature short. Therefore, it will make a focal length short. Also, the small on-chip micro lens faces a problem of focal length that a focal length near the edges of the on-chip micro lens is shorter than that of the axis of the on-chip micro lens.
For example, a lens for a conventional camera is made into an aspheric lens so as to solve the problem of focal length. Therefore, it is preferable to make an on-chip micro lens used for a solid-state imaging device into an aspheric lens. However, it is very difficult to form an aspheric lens as an on-chip micro lens according to a prior manufacturing method.
It is an object of the present invention to provide a solid-state imaging device, wherein a micro lens can gather light onto a photoelectric conversion unit, manufactured without a complex step such as forming an inner lens.
It is another object of the present invention to provide a solid-state imaging device that can effectively lead incident light onto a pixel.
According to one aspect of the present invention, there is provided a solid-state imaging device comprising: a semiconductor substrate which demarcates a two-dimensional surface; a multiplicity of photoelectric conversion units configured in a multiplicity of rows and columns on the surface of said semiconductor substrate; a light shielding film having openings formed above said semiconductor substrate, each of the openings is formed on each of said photoelectric conversion unit; a planarizing insulating film formed on said light shielding film; micro lenses formed on said planarizing insulating film, each micro lens is formed just above each of said opening; and a modifying film having one layer or a plurality of layers formed directly on said micro lenses and having a top surface with different curvature from that of a top surface of the micro lenses.
According to another aspect of the present invention, there is provided a method of manufacturing a solid-state imaging device comprising the steps of: (a) forming a multiplicity of photoelectric conversion units configured in a multiplicity of rows and columns on a surface of a semiconductor substrate which demarcates a two-dimensional surface; (b) forming a light shielding film having openings, each of which is formed on each of said photoelectric conversion unit, above said semiconductor substrate; (c) forming a planarizing insulating film on said light shielding film; (d) forming micro lenses, each of which is formed just above each of said opening, on said planarizing insulating film; (e) forming a modifying film having one layer or a plurality of layers on said micro lenses; and (f) curing said film having one layer or a plurality of layers formed at said step (e) by heating.
According to another aspect of the present invention, there is provided a method of manufacturing a solid-state imaging device comprising the steps of: (a) forming a multiplicity of photoelectric conversion units configured in a multiplicity of rows and columns on a surface of a semiconductor substrate which demarcates a two-dimensional surface; (b) forming a light shielding film having openings, each of which is formed on each of said photoelectric conversion unit, above said semiconductor substrate; (c) forming a planarizing insulating film on said light shielding film; (d) forming color filters in a plurality of colors on said planarizing insulating layer; (e) forming micro lenses, each of which is formed just above each of said openings, on said color filters; (f) forming a modifying film having one layer or a plurality of layers on said micro lenses; (g) removing part of said modifying film according to colors of said color filters by patterning; and (h) curing said modifying film formed at said steps (f) and (g) by heating.